Our present invention relates to a drawing device for the drawing of elongated material, especially with cross section reduction in a drawing stage of a drawing line. More specifically, the invention relates to the drawing of elongated metal workpieces from billets or bars utilizing a drawing device having at least one drawing carriage, a drive for the carriage and, if appropriate, a drawing die for shaping and reducing the cross section of the workpiece.
Drawing machines are used for the drawing of elongated metal workpieces like tubes, bars or rods, through a tool or die with reduction in cross section at the tool and, if desired, shaping of the workpiece to a particular profile. The workpieces can be referred to as structural shapes or as profiles. Drawing machines of the type described can be so-called continuous drawing machines in which the length of the workpiece can be many times greater than the length of the machine and the workpiece can emerge more or less continuously. Drawing machines can also be discontinuous drawing machines capable of drawing a workpiece of only a limited length and sometimes referred to as drawing benches.
One example of a continuously working linear drawing machine is found in DE 28 52 071. This patent document discloses a carriage-type drawing machine in which two drawing slides or carriages are moveable parallel to the drawing direction along a guide on a machine frame. These carriages are movable back and forth and are provided with means for engaging the workpiece in a hand-to-hand mode so as to pull the workpiece more or less continuously through the die. The hand-to-hand machine is generated by double-arm levers which are connected to the slides or carriages and themselves are controlled by a double-curve cam which produces the back and forth motion of each carriage.
Another driving system for a drawing machine is disclosed in European patent document EP 0 371 165 which provides a rotating drum which has a cam formation in the form of a rib of its periphery to produce the opposite movements of the drawing slides or carriages. The short strokes of the curves means that each stroke will consist basically and predominantly of an acceleration segment and a braking segment. To ensure operation with a high mean drawing speed, a very high stroke frequency should be used. The stroke frequency, however, cannot be increased without limits since it is restricted by the fact that there is significant inertia at the reversal points.
In drawing processes which involve a plurality of drawing machines in succession and reduce the cross section of a workpiece in a number of stages, it is customary to reel up the driven product at the end of the drawing line. For this purpose, the drawing machines must be coupled together (see European patent document EP 0 182 922 A1). This can be achieved with a buffering of the length of the workpiece between drawing stages, e.g. by deflecting the workpiece out of its linear lie between the output side of one machine and the input side of the next machine.
When two or more such drawing machines are used together with loop-type buffering of the length of the workpiece, it is necessary in prior art systems to impart a bend to the workpiece which may impose requirements on the further processing. This applies also to systems in which the workpiece may be reeled or wound up between stages.
It is, therefore, the principal object of the present invention to provide a drawing machine, device or unit which is simple and thus of low capital cost, can be used effectively in drawing lines having multiple units and can have a high production rate with minimum operating and capital cost.
Another object of this invention is to provide an apparatus for drawing an elongated workpiece which represents an advance over the prior art systems described.
Another object of this invention is to provide a drawing apparatus which is free from drawbacks of prior art systems including those mentioned earlier.
These objects and others which will become apparent hereinafter are achieved in accordance with the invention in a modular drawing apparatus for drawing an elongated workpiece, especially a metal workpiece, which comprises:
at least one elongated path-forming module alignable contiguously and directly with others of the path-forming modules to define an uninterrupted elongated travel path;
at least one holder module engaged with the at least one elongated path-forming module and constructed and arranged for selective attachment to the others of the path-forming modules;
a drawing die mounted in the at least one holder module; and
a drawing carriage provided with a device engageable with the workpiece and a part carrying the device and displaceable along the path relative to the at least one elongated path-forming module, the part and the path-forming module forming mutually interactive elements of a linear motor for direct displacement of the carriage along the path.
The drawing line embodying the invention can comprise two drawing apparatuses as described in respective drawing stages and located directly abutting one another contiguously along an aforementioned path.
According to the invention the drawing unit or puller for the workpiece is assembled in a modular manner from a plurality of modules which can be identical to one another and utilized interchangeably. These modules include at least one path-forming module which can be joined directly to at least one other path-forming module to form a continuous linear path along the drawing line. The term xe2x80x9cdirectly connectablexe2x80x9d is here used to signify that the path-forming modules adjoin one another in a direct end-to-end relationship without any intervening elements and are coupled together so as to be contiguous in their adjoining regions.
The apparatus includes at least one holder module for fastening a drawing die to the drawing unit. The holder module, which can be used interchangeably with other holder modules and can receive any of a number of dies which may be used in succession along the line, has formations which are complementary to those of each path-forming module so that any one of the path-forming modules may receive such a holder module, preferably at an upstream end thereof with respect to the drawing direction. According to the invention the drive means for the drawing carriage is a linear motor with the part carrying the workpiece clamp to the drawing carriage and the path-forming module constituting mutually interactive elements of the linear motor which directly displaces the carriage along the path.
The linear motor referred to herein is an inductive electrical linear motor of the type in which one of the elements forms the so-called stator and which is relatively stationary while the other element forms the armature and is linearly-shiftable by the inductive forces which are generated.
The coils for producing the electromotor force can be provided on one of the elements and the magnetic fields coil can produce eddy currents in the other element so that the magnetic field thereby induced can react with the electromagnetic field to provide the linear force along the path displacing the carriage to draw the workpiece through the die.
Since the drawing unit of the invention is itself of modular construction and is comprised of individual path-forming modules which can be joined together to form the path and in its simplest form has only one such path-forming module, each path-forming module can have a holder module for receiving a respective die. The holder module can be removed from the path-forming module and inserted interchangeably into a path-forming module further downstream. In addition the die may be removably mounted in the holder module. The result is a construction in which holder modules may be provided anywhere along the path and the retaining formations for the holder module can be located at various locations along each path-forming module so as to provide a drawing apparatus of a higher degree of versatility.
Thus for example, any path-forming module can be equipped with one or more holder modules and not every holder module need contain a holder module or die. The drawing device will also include at least one drawing carriage forming the linear motor with the path and thus the travel path itself forms part of the linear motor.
Apart from the modular construction of the drawing unit itself, each linear motor drive for a respective drawing carriage can be of modular construction so that a linear motor can encompass a linear motor complex for a drawing carriage that includes one or more linear motor units. As noted, one such linear motor unit will have a primary and secondary. The primary, of course, including the coils for generating the electromagnetic field in response to electrical energization of the stationary part, either the primary or the secondary, of the respective linear motor unit is integrated in the path-forming module. The movable part is connected with the carriage and will be the other of the secondary and primary. Depending upon the power required for the respective drawing carriage, the linear motor complex will have an appropriate number of linear motor units.
The module construction of the drawing device and the module construction of the linear motor drive for each carriage can be variably assembled for each drawing unit so that a large variety of configurations with different drawing capacities for different products to be drawn can be assembled at minimum cost for construction, assembly and operation.
The path-forming module can be so configured that it is capable of direct connection with at least one further path-forming module to a continued path for the carriage. The drawing unit can thus be assembled to any requisite length and can accommodate a number of drawing carriages displaceable with the same stroke or so as to provide a greater stroke to one or a lesser number of drawing carriages.
The use of a linear electric motor, eliminates the need to limit the stroke length for travel of each individual carriage. Linear motors provide exact control or regulations of the pull on the workpiece, provide rapid acceleration and rapid braking. The use of a greater stroke means that the average speed will be greater since the acceleration and braking segments can be proportionally smaller. It is therefore possible to operate the respective carriages in the forward and rearward movements with different speeds and thus bring each carriage back more quickly into a position in which it engages the workpiece for the pulling operation.
Preferably the stationary secondary of the linear motor drive for the respective drive carriage is configured as a central rail whereby the drawing carriage is displaceable on outer guide rails. Alternatively the stationary secondary part can be formed as two parallel outer rails of a track module and the guide can be formed as the middle rail. Preferably, moreover, this guide is also a modular construction from a plurality of individual guide modules which are assembled together to form the guide. In this manner the path or guide of a drawing unit, depending upon desire, can be extended or shortened as a function of the number of drawing carriages used.
The length of a path-forming module can correspond, according to the invention, to the length of a guide module to allow a change in the length of the line with a minimum of expense.
The individual path-forming modules, by analogy to the individual guide modules, can all have the same length or can be of different lengths, each a whole number of times a modular length. In this manner the operator can determine which individual modules of a unit must be assembled together to satisfy any particular requirement. The guide module lengths can be matched to the path-forming module lengths.
The individual path-forming modules, as has been noted, can be provided with formations to allow holder modules to be mounted at various locations along the length of the path-forming module and thus to allow the placement of the die at either of several locations in the path-forming module. The formations or arresting parts of the holder modules can be projections which engage in grooves of the path-forming module to allow positioning of the dies where desired.
The invention also is a drawing line of modular construction which itself is formed of at least two drawing units each comprising at least one path-forming module and at least one and preferably two drawing carriages and a holder module for at least one die. The line can thus comprise a continuous path through which the workpiece is drawn in two or more stages.
By contrast to prior art systems as has been described, the two drawing units are directly adjacent one another, i.e. contiguous and the drawing carriages of the two units are operated independently or in a coupled relationship to eliminate the need for a buffer loop, in spite of the fact that the downstream unit must operate at a linear speed greater than that of the upstream unit. For this purpose the drawing line has a computer for controlling the linear motor of the respective drawing units and signal lines for transmitting power to the respective linear motor or carriages or for transmitting inputs to the computer to coordinate the back and forth movement carriages and thus to coordinate the movements of the carriages in the two units with one another. The modular construction, of course, allows a high versatility in creating the drawing line.
The linear motor drive of the respective slides can be so precisely and individually controlled that there is no need at all for buffer zones. The result is a cost saving in addition to the increased compaction of the overall line since neither buffer zone or compensating or equalizing zones are required. Most workpieces can be fabricated in a single pass through a number of stages.
It is especially preferred to assemble the modules into a drawing line with combined predrawing and drawing carriages which in a first stage effect a predrawing step and in a subsequent stage a main drawing operation alone or in combination with further drawing carriages.